1. Field of the Invention
The invention relates to the field of power electronics.
It is based on an insulated-gate bipolar transistor (IGBT) as claimed in the preamble of the first claim. It furthermore relates to a method for producing an IGBT according to the invention.
2. Discussion of Background
Such an IGBT has already been described in EPA20 405 138.
This IGBT comprises between two main areas, one of which is allocated to a cathode and the other one of which is allocated to an anode, a number of differently doped semiconductor layers. Starting with an n-doped semiconductor substrate, an n+-type barrier layer and a p-type emitter follow in the direction of the anode. The p-type emitter is covered with the anode metallization which forms the anode. From the semiconductor substrate towards the cathode, p-type collector regions, which are preferably of strip-shaped design, are diffused into the first main area. In addition, a number of source regions which are constructed as islands and reach from a channel region, which comprises a part of the collector region underneath the gate electrode, to just in front of the center of the collector strip are in each case inserted into these collector regions. In one collector strip, two source regions are arranged alternately opposite one another from both sides of the collector strip edge so that only one channel region is produced in section transversely to the collector strip. The source regions of one side of the collector strip in each case exhibit a distance D.
It is then the aim of the patent application initially mentioned to specify an IGBT and a method for producing the latter which exhibits high short-circuit strength and high insensitivity to latch-up. This is essentially achieved by the fact that the distance D between two source regions is selected to be greater than twice the width of the channel region.
However, there is still a problem with this IGBT in that the source islands only extend into the collector region up to a certain depth. If the mask for producing the source region is thus slightly misaligned, source islands are obtained which extend farther on one side of the collector region and not as far into the collector region on the other side. Instead, the channel region is narrower on this side. Holes which flow from the anode through to the cathode underneath the source regions are accordingly exposed to a different resistance. Similarly, the latch-up resistance also fluctuates with the misalignment of the source islands.
As a consequence of this, an inhomogeneous turn-off current distribution is obtained. In the case of an inhomogeneous turn-off current distribution, however, the performance of the component is determined by the weakest point of the total power component. The component can therefore only be loaded with the power which the weakest point can be expected to handle. In the final analysis, therefore, a component having reduced efficiency is obtained as a consequence of the misalignment of the source islands.